1. Field of the Invention
The invention is related to electrical cables and in particular to a wire wound core ignition cable for internal combustion engines.
2. Description of the Prior Art
Ignition cables having a wire wound core provide a means for accurately and reliably controlling the resistivity of a finished product. The current ignition cables having a wire wound conductive core are difficult to strip to make electrical connection between the wire and a terminal. Frequently the wire, because it is not protected, is pulled out of the end of the cable during the stripping operation resulting in the formation of an unwanted and undesirable wire "tail". If this "tail" is not properly trimmed prior to attachement of the terminal, it can lead to premature dielectric failure of the terminal assembly or cause arcing between the tail and a ground plane.
A typical example of such a wire wound cable is taught by Miyamoto et al in U.S. Pat. No. 4,435,692 and Coffey et al in U.S. Pat. No. 4,700,171. Miyamoto et al teach a wire wound ignition cable in which the resistance wire is wound over a ferrite core. The resistance wire and ferrite core are coated by an extruded layer of a blend of polyethylene and ethylene propylene diene. Coffey et al disclose an ignition cable comparable to that taught by Miyamoto in which a core is formed by dip coating a glass fiber strength member with an insulating layer containing magnetic particles such as iron oxide. The core is then helically wrapped with a resistance wire. The resistance wire is then dip coated with a semi-conductive thermoplastic polymer. The semi-conductive thermoplastic polymer contains carbon particles and release agents which allow subsequently applied insulating layers to be stripped cleanly.
The problem with the ignition cable taught by Coffey et al is that the semi-conductive thermoplastic is unstable at relatively low temperatures. Therefore, the temperature range of the ignition cable taught by Coffey is limited. The invention is a solution to the temperature stability of the ignition cable which allows it to be used at temperatures up to 500.degree. F.